In the chemical and petroleum industries, fluid catalytic methods are employed in which finely divided catalyst particles are maintained suspended in a gas in the so-called "fluid state" under reaction conditions. Particles in the fluid state act in many ways like a liquid and undergo hindered settling. Thus, they may be conveyed from one vessel to another through a conduit, they develop a pressure head, etc.
Large units can operate continuously on-stream for extended periods of time under closely controlled conditions by employing fluid catalytic procedures. Catalysts in such units in processes where deposition of undesirable coke or other contaminant is encountered during the reaction state may be maintained at a predetermined level by continuously circulating the catalyst from the fluid reactor to a regenerator where such coke or contaminant is removed as by oxidative combustion. Fluid units of large capacity, such as through-put of 60,000 barrels or more of charge per day, are intended to operate on-stream for periods of as long as a year or more without being shut down.
Various applications involve high temperature operations in the chemical processing and petroleum refining arts including use in a converter such as a fluid catalytic cracking unit or a fluid catalytic hydroforming unit of conventional design having superimposed contact chambers in which the catalyst is maintained in a state of phase separation comprising an upper diffuse phase and a lower dense pseudo-liquid phase, the catalyst being withdrawn from the lower dense phase of the upper chamber through a vertical internal standpipe and discharged at a low point within the dense phase of the lower chamber and, after suitable treatment in the lower chamber, being returned upwardly through an internal vertical carrier line to the dense phase of the upper chamber.
By passing catalyst by gravity flow from an upper chamber to a lower chamber through a standpipe and passing the catalyst from the lower chamber to the upper chamber through a carrier line by aspiration into a stream of the gas to be contacted in the upper chamber, a continuous flow of the mixture through the carrier line is produced. In those cases where a regeneration zone is superimposed upon a conversion zone, the gas introduced into the carrier line is ordinarily air or other oxygen-containing gas. In those cases where the conversion zone is superimposed upon the regeneration zone, the gas introduced into the carrier line is a stream of vaporous hydrocarbons.
Flow control of catalyst from the standpipe into the dense phase of the lower chamber and from the latter into the carrier line for conveyance into the upper chamber is obtained by the use of plug valves positioned in the lower chamber engageable with the lower ends of the transfer lines, the plug valves having elongated valve stems extending through the chamber wall controlled in their longitudinal movement by external mechanical or manual operating means. These plug valves are used in oil refineries in controlling the flow of catalyst into a reaction chamber which is subject to temperature extremes, for example, in the range of 1500.degree. F., as well as in other industrial applications wherein the valves are subject to oppositely directed displacements due to thermal expansion and spring forces.
Current vessel or container mounted plug valves for high temperature catalyst service are equipped with guide liners and bleed rings which guide the stem or stem tube and are purged continually by a purge medium. The purpose of the purge medium is to keep the catalyst (fluidized particles) out of the guide liners and bleed rings utilized with these valves.
There are a number of problems associated with plug valves having conventional continuous purging of bleed rings and guide liners. The valve stem or stem tube rubs against the guide liners and cause damage possibly resulting in sticking of the valve. The purges often do no operate properly, that is, the purging is excessive or inadequate. In the case of excessive purging, the guide tube, guide liners, and stem or stem tube erode. In the case of inadequate purging, the solid particles enter the guide liners and cause sticking of the valve stem or stem tube. Also, erosion of the plug closure member and valve seat are caused by high velocities of catalyst flow in the chamber or vessel in which the plug valve is disposed.
There has been a long felt need to overcome the problems associated with continuous purging of prior art plug valves as mentioned above. It is desirable and advantageous to provide a plug valve which overcomes the above-mentioned problems.